Method of making preformed sound absorbing units



Aug. 4, 1936. H. E. HoLcoMB METHOD OF MAKING PREFORMED SOUND ABSORBING UNITS Filed oct. 19, 1932 eeegoaeaan eoeunaeose INVENToR Har/y Ef golcomb. 4

BY @74 @ff/@Mama ATTORNEY Patented Aug. 4, 1936 UNETED SIA'EES Meer arriba METHOD F MAKING PREFORMED SOUND ABSORBHNG UNTS Application October 19, 1932, Serial No. 638,501

3 Claims.

This invention relates to a preformed soundabsorbing unit and method of making the same. The invention comprises the novel features hereinafter described or claimed, including a 5 preformed unit comprising a sound-absorbing element, a perforated face molded onto the sound-absorbing element and hardened in situ, in integral union with the said element. The invention comprises also a method of producing a perforated sheet material, suitable for use as the facing of the sound-absorbing unit, by casting a composition adapted to be hardened, causing readily deformable perforating elements, such as rubber pegs or projections from a exible sheet, 15 to penetrate through the casting, allowing the casting to harden, and then separating the deformable perforating elements from the hardened casting.

The invention is illustrated in the drawing in 2O which Fig. 1 shows a perspective view of the preferred embodiment of the product of the present invention, with parts broken away for clearness of illustration; and

25 Fig. 2 shows a similar view of a mold assembly and materials therein, as used in making the improved article of the present invention.

In Figure l there is shown a sound-absorbing element I, a perforated sound-.permeable or 30 sound-transmitting face 2, provided with perforations 3, of size and spacing adapted to admit incident sound readily. The unit may have beveled edges 4, andv sealing and reenforcing edge elements 5 of a composition similar to that com- 35 prising the face portion.

The sound-absorbing element is suitably one that is semi-rigid and adapted to minimize the tendency to breakage of a more or less fragile facing element when united thereto. There has m been used to advantage a preformed sound-absorbing pad or sheet of mineral wool, such as one consisting essentially of rock wool and a small proportion of starch as the binder and stiffening agent. Other fibrous materials and other N binders may be used, as, for example, asbestos fibers and resinous chlorinated diphenyl or casein binder.

The method of making the preferred form of my improved product is described in connection 50 with Fig. 2.

There is provided a mold 6, suitably with removable walls l. Into this mold and over the bottom thereof is laid a flexible mat B, with readily deformable projections or teats 9, suitably a 55 rubber sheet with upstanding rubber pins thereon. Over the rubber mat provided with the readily deformable rubber penetrating and perforating elements is cast a composition lll adapted to be hardened, say one comprising a hydraulic cementitious material. constitutes an especially suitable casting composition, for the purposes of the present invention. The composition is cast to a depth not exceeding the length of the penetrating elements, so that the said elements extend through the casting from face to face. Any of the casting composition that coats the projecting ends of the penetrating elements may be removed therefrom, as by being brushed off. Promptly after the casting is made and the relatively clean ends of the penetrating elements are exposed, a sound-absorbing element, such as a preformed block of rock wool with starch binder, is pressed down upon the tops of the penetrating pins and the I upper surface of the casting. suitably, the rock 20 wool block has dimensions of face that are somewhat smaller than the corresponding dimensions of the inside of the mold, whereby, when the block is placed in the mold and pressed down into position, some space is left around the block, inside the side walls of the mold. Into this space, there is cast composition of the kind used to form the face. This produces edge elements I2 that, after hardening, are integrally united to the edges of the block. The cast composition is then caused to harden, as by being allowed to stand until the cementitious material therein sets.

Following the step of hardening, the penetrating elements are separated from the hardened product, as by removing the casting from the mold and then stripping the readily deformable rubber mat with its rubber projections from the casting. During this stripping operation the rubber stretches or undergoes other deformation that facilitates its separation from the holes in the casting, without cracking the casting or chipping the material around the edges of the holes.

In the above procedure, it has been found desirable to observe certain conditions. The mat and perforating elements are wetted with water before the casting is made thereover; this preliminary wetting contributes to the adhesion of the plaster and smoothness of the casting over the rubber. The plaster composition as cast is relatively thin. After being cast, it is vibrated for a short time, to cause the rise of air bubbles away from its lower surface.. Also, the plaster and backing pad may be kept in slightly dished shape, during casting and hardening, to allow for a subsequent slight warping.

Plaster mixed with water With the procedure described above, interesting results are obtained. When the sound-absorbing backing is pressed against the upper face of the casting and the penetrating elements, some of the composition, which is uld at this stage, penetrates to a limited extent within the surface of the porous sound-absorbing backing, except at positions where the penetration is impeded by the close contact between the backing and the tops of the penetrating elements. The penetrating elements thus prevent the continuous coating of the sound-absorbing element with the casting composition and provide that, in the nished article, there is communication between the perforations in the face and the pores in the backing element. If it is desired to improve this communication, the finished unit may be subjected to a punching operation in which pins are inserted through the perforations made as described and into the backing, to break the plaster seal that may extend over the bottoms of some of the perforations. In the hardening operation the composition comprising the face and the portion thereof that has penetrated Within the porous backing element hardens in situ. This gives not only integral union of the two elements to each other, but also a very desirable reenforcing and supporting action of the backing element, over a substantial area of surface thereof, upon the more fragile face. The casting around the edges of the backing element, if used, becomes united to the edges and serves, in the finished product, to reenforce and shape the edges of the unit and seal them against circulation of air therethrough.

The product of the present invention has numerous advantages over previously known structures, in addition to those advantages which have been indicated already.

The unit may be preformed at the factory in sizes convenient for installation in thev ceiling or walls of a building. rIhe units are relatively light in Weight although they have faces possessed of the density, smoothness, and impermeability of ordinary plaster, for example, except as the continuity of the face is broken at predetermined intervals by the perforations. 'I'he face may be decorated, as by painting or lacquering, without preventing the satisfactory transmission of sound through the face of the material. With the backing of rock wool, the product is very effective in absorbing sound incident upon its face and is nre-resistant.

A material other than rubber that meets the requirements for the chief ingredient of the exible mat and perforating elements is chloro-2- butadiene-1,3 polymerized to a rubber-like material, as described by Carothers and others in the Journal of the American Chemical Society, vol. 53, pages 4203-6, 1931. The substitution of this material for rubber is desirable when the composition that is molded around the deformable perforating elements is one that is subsequently hardened at an .elevated temperature, say, a plastic composition comprising a phenolaldehyde condensation product.

The term preformed, as applied to the soundabsorbing element of the structure unit, signifies that the element is formed before the facing is molded thereon.

The details that have been given are for the purpose of illustration and not restriction, and many variations therefrom may be made without departing from the spirit and scope of the invention.

What I claim is:

1. The method of making an acoustical unit having a perforated face which comprises forming acastable composition adapted to be shaped into asheet and hardened, casting the composition upon a exible mat provided with readily deformable upstanding projections of length adapted to extend through the casting, impressing a sound-absorbing element upon the exposed surface of the casting, allowing the casting to harden and then separating the flexible mat and projections from the hardened casting.

2. In the method described in the preceding claim the improvement comprises wetting the said upstanding projections before casting the said composition thereover.

3. The method of making an acoustical unit having a perforated face which comprises forming a castable composition adapted to be shaped into a sheet and hardened, casting the composition upon a flexible mat provided with readily deformable upstanding projections of length adapted to extend through the casting, impressing, upon the exposed surface of the casting, a fibrous readily penetrable sound-absorbing element so as to cause the said projections to contact with the said element and to cause the said composition to impregnate the surface portion of the said element at positions between the places of said contact with the projections, allowing the casting to harden and then separating the flexible mat and projections from the hardened casting.

HARRY E. HOLCOMB. 

